Cyclohexanone is an important material in the chemical industry and is widely used in, for example, production of phenolic resins, bisphenol A, caprolactam, adipic acid, and plasticizers. One method for making cyclohexanone is by hydrogenating phenol.
Currently, a common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of cumene to the corresponding hydroperoxide, and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. The separated phenol product can then be converted to cyclohexanone by a step of hydrogenation.
It is known from, e.g., U.S. Pat. No. 6,037,513, that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a bifunctional catalyst comprising a molecular sieve of the MCM-22 type and at least one hydrogenation metal selected from palladium, ruthenium, nickel, cobalt, and mixtures thereof. This reference also discloses that the resultant cyclohexylbenzene can be oxidized to the corresponding hydroperoxide, which can then be cleaved to produce a cleavage mixture of phenol and cyclohexanone, which, in turn, can be separated to obtain pure, substantially equimolar phenol and cyclohexanone products. This cyclohexylbenzene-based process for co-producing phenol and cyclohexanone can be highly efficient in making these two important industrial materials. Given the higher commercial value of cyclohexanone than phenol, it is highly desirable that in this process more cyclohexanone than phenol be produced. While this can be achieved by subsequently hydrogenating the pure phenol product produced in this process to convert a part or all of the phenol to cyclohexanone, a more economical process and system would be highly desirable.
One solution to making more cyclohexanone than phenol from the above cyclohexylbenzene-based process is to hydrogenate a mixture containing phenol and cyclohexanone obtained from the cleavage mixture to convert at least a portion of the phenol contained therein to cyclohexanone. However, because the phenol/cyclohexanone mixture invariably contains non-negligible amounts of (i) catalyst poison component(s) (such as S-containing components) that can poison the hydrogenation catalyst, and (ii) cyclohexylbenzene that can be converted into bicyclohexane in the hydrogenation step, and because hydrogenation of the phenol/cyclohexanone/cyclohexylbenzene mixture can also lead to the formation of cyclohexanol, resulting in yield loss, this process is not without challenge. In short, the unconventional feed to a phenol hydrogenation process, produced by the aforementioned route including hydroalkylation of benzene, presents a great deal of challenges to maintaining the desired activity of phenol hydrogenation catalyst, and the desired selectivity to cyclohexanone.
Recently, the present inventors have found that, in the process including cyclohexylbenzene oxidation followed by acid cleavage of the cyclohexylbenzene hydroperoxide process for making cyclohexanone (hereinafter called the “CHB-route”), 2-cyclohexenone and 3-cyclohexenone are produced due to various side reactions that may occur in the various reactors, especially the cleavage reactor, and one or both of them can be present as impurities in the cyclohexanone-containing products. The presence of 2-cyclohexenone and 3-cyclohexenone impurities at elevated concentrations can cause various issues in downstream use of the cyclohexanone-containing products, such as the manufacture of caprolactam. Therefore, there is a need to abate the concentration of both 2-cyclohexenone and 3-cyclohexenone from the cyclohexanone product.
Some references of potential interest in this regard may include: U.S. Pat. Nos. 3,076,810; 3,322,651; 3,998,884; 4,021,490; 4,200,553; 4,203,923; 4,439,409; 4,826,667; 4,954,325; 5,064,507; 5,168,983; 5,236,575; 5,250,277; 5,362,697; 6,015,927; 6,037,513; 6,046,365; 6,077,498; 6,215,028; 6,730,625; 6,756,030; 7,199,271; 7,579,506; 7,579,511; 8,222,459; 8,389,773; 8,618,334; 8,772,550; 8,802,897; and 8,921,603. Other references of potential interest include WIPO Publication Nos. WO 97/17290; WO 2009/128984; WO 2009/131769; WO 2009/134514; WO 2010/098916; WO 2012/036820; WO 2012/036822; WO 2012/036823; WO 2012/036828; WO 2012/036830; WO 2014/137624; and WO2017/023430. Further references of potential interest include EP 0 293 032; EP 0 606 553; EP 1 575 892; JP 434156 B2; as well as Alexandre C. Dimian and Costin Sorin Bildea, Chemical Process Design: Computer-Aided Case Studies, pp. 129-172 (Wiley, 2008); Van Peppen, J. F. et al., Phenol Hydrogenation Process, in Catalysis of Organic Reactions, pp. 355-372 (1985, ed. R. L. Augustine); Díaz et al., Hydrogenation of phenol in aqueous phase with palladium on activated carbon catalysts, CHEM. ENG'G J. 131 (2007) at 65-71; and Gonzalez-Velazco et al., Activity and selectivity of palladium catalysts during the liquid-phase hydrogenation of phenol: Influence of temperature and pressure, INDUSTRIAL & ENG'G CHEM. RESEARCH (April 1995), Vol. 34, No. 4, p. 1031.